In particular, the present invention relates to a method for preparing a deposition from the gas phase under vacuum, wherein a target is used as the material source and particles from its surface fly to the substrate and are deposited on the latter. A reactive gas is frequently used, the atoms and/or molecules of which react with the particles so that the corresponding chemical compound is deposited on the substrate. This is then referred to as a reactive coating process.
Several such coating processes are well-known. As examples, magnetron sputtering and spark evaporation should be mentioned. The respective target surfaces are exposed to different ambient influences. For example, in many cases a chamber door must be opened for charging and discharging the coating chamber, so that the target surface is exposed to normal room atmosphere. Sometimes, when target poisoning has occurred due to the reactive gas, the target surface must also be exposed to special mechanical treatment, such as sandblasting. All these are circumstances that lead to the target surface differing from one coating pass to the next due to different environmental influences. If such a target surface were to be immediately used for coating, non-reproducible results would be the consequence. In particular, the beginning of the coating is not reproducible, which, among other things, has an essential influence on layer adhesion. Particularly in the field of wear protection, however, such incalculable differences in adhesion and in other layer properties are intolerable.
To counteract this, after closing and evacuating the coating chamber, coating is first started in such a way that by means of a shield the coating material is prevented from impinging and depositing on the substrate for a certain period of time. Such a process is called target conditioning.
Target conditioning can sometimes take half an hour or longer. FIG. 1 shows the optical signal of plasma burning in front of a target containing chromium during this conditioning. It can be seen quite clearly that the OES signal only stabilizes after about 30 minutes, which is a sign that conditioning is finished and no further essential changes will take place on the target surface. Consequently, the time required therefor leads to an extension of the coating period measured from the charging of the coating plant to discharging after coating.
It has already been mentioned that good layer adhesion is necessary for many applications. To achieve good layer adhesion, for example, the substrate has to have a clean surface. Cleaning the substrate to be coated must always be carried out outside of the coating chamber. However, some preparatory treatment steps of the substrate surface are only carried out within the chamber and under a vacuum after the coating chamber is closed. It is particularly advantageous to expose the substrate surface to an etching process shortly before coating, and particularly preferably by means of a plasma, i.e. a plasma etching process. Herein, it is quite common to remove as much as 1 μm from the surface. In this way, the last of the dirt particles are removed, and with certain substrate materials there is a near-surface concentration depletion, thus strongly increasing the adhesion of the layer material applied in the subsequent coating step. In some cases the surface of the substrate is activated by the pretreatment and, in particular, by the plasma etching, which in turn leads to better adhesion. It is a drawback, however, that this process step also takes considerable time so that after the coating chamber is closed and the evacuation started, it can sometimes take up to an hour before the actual coating can begin. The long waiting times have a direct effect on the overall duration of the method and thus the manufacturing cost of such layers.
It would thus be desirable to have a method that takes substantially less time without any deterioration of the product quality and, in particular, of the adhesion of the layer on the substrate.
The object of the present invention is based on this need.